Not Applicable
1. Field of the Invention
The invention relates to a novel process for the manufacture of very low molecular weight polyphenylene ether resin, typically within the intrinsic viscosity range of about 0.08 dl/g to about 0.16 dl/g as measured in chloroform at 25xc2x0 C.
The invention also relates to the polyphenylene ether resin made by the process as well as blends and articles containing the polyphenylene ether resin made by the process.
2. Brief Description of the Related Art
Polyphenylene ether resins (hereinafter xe2x80x9cPPExe2x80x9d) are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Furthermore, the combination of PPE with other resins provides blends which result in additional overall properties such as chemical resistance, high strength, and high flow.
The processes most generally used to produce PPE involve the self-condensation of at least one monovalent phenol in the presence of an oxygen containing gas and a catalyst comprising a metal amine complex to produce resins typically within the intrinsic viscosity range of about 0.35 dl/g to about 0.65 dl/g as measured in chloroform at 25xc2x0 C.
These processes are typically carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. The catalyst metal, after being converted into a soluble metal complex with the aid of a chelating agent, is removed from the polymer solution with standard extraction techniques, such as liquid-liquid extraction. The PPE polymer can be isolated in a variety of methods although generally by anti-solvent precipitation.
As new commercial applications are sought for PPE, a wider range of intrinsic viscosity resins, especially lower intrinsic viscosity resins, have been desired. As intrinsic viscosity decreases in PPE resins, the level of hydroxyl groups increases and the rheological properties change dramatically (lower viscosity as intrinsic viscosity decreases) as compared to current commercially available high molecular weight PPE produced by the methods previously described. The physical properties of PPE remain highly desirable and sought after in applications such as, for example, adhesives, sealants and gels based on SBC, SBR, or epoxies for automotive, housing, cabeling, membranes and electrical applications. Also, epoxy based composites for aerospace, automotive structural members and sporting equipment are desirable applications as are electrical laminates, and IC encapsulation materials based on epoxies and unsaturated polyesters. Friction materials and abrasives compounds based on phenolic are also sought after. PPE is also useful as an additive in various thermoplastic and thermoset materials including, e.g., polypropylene, polystyrene, ABS, polycarbonate, polyetherimide, polyamides, polyesters, and the like and also thermosetting resins such as, for example, epoxies, unsaturated polyesters, polyurethanes, allylic thermosets, bismaleimides, phenolic resins, and the like. Varying enhanced properties may be improved in different systems such as, for example, improved heat performance, flame retardancy improvement, decrease of electrical properties like Dk and Df, decrease in moisture absorption, increased creep resistance, thermal expansion reduction, chemical resistance to acids and bases, for various applications such as, for example, automotive and house hold and electrical goods.
It is therefore apparent that a need exists for the development of processes for the manufacture of very low molecular weight polyphenylene ether resin, typically within the intrinsic viscosity range of about 0.08 dl/g to about 0.16 dl/g as measured in chloroform at 25xc2x0 C.
The needs discussed above have been generally satisfied by the discovery of a process for preparing PPE having an intrinsic viscosity within the range of about 0.08 dl/g to about 0.16 dl/g as measured in chloroform at 25xc2x0 C. comprising oxidative coupling in a reaction solution at least one monovalent phenol species using an oxygen containing gas and a complex metal catalyst to produce a PPE having an intrinsic viscosity within the range of about 0.08 dl/g to about 0.16 dl/g as measured in chloroform at 25xc2x0 C.; removing at least a portion of the complex metal catalyst with an aqueous containing solution; and isolating the PPE through devolatilization of the reaction solvent.
The description that follows provides further details regarding various embodiments of the invention.
Not applicable
This invention provides for a process for the preparation of low molecular weight PPE, preferably having an intrinsic viscosity between about 0.08 dl/g and 0.16 dl/g, by oxidative coupling at least one monovalent phenol species, preferably at least a portion of which have substitution in at least the two ortho positions and hydrogen or halogen in the para position, using an oxygen containing gas and a complex metal-amine catalyst, preferably a copper (I)-amine catalyst, as the oxidizing agent and extracting at least a portion of the metal catalyst as a metal-organic acid salt with an aqueous containing solution, and isolating the PPE through devolatilization of the reaction solvent. In one embodiment, the process affords a PPE that has less than a 10% increase, preferably less than 5% increase in intrinsic viscosity after heating into the melt phase. In another embodiment, the process affords a PPE that has less than a 10% decrease, preferably less than 5% decrease, most preferably less than 3% decrease in intrinsic viscosity after an equilibration step following the oxidative coupling reaction.
The PPE employed in the present invention are known polymers comprising a plurality of structural units of the formula 
wherein each structural unit may be the same or different, and in each structural unit, each Q1 is independently halogen, primary or secondary lower alkyl (i.e., alkyl containing up to 7 carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each Q2 is independently hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for Q1. Most often, each Q1 is alkyl or phenyl, especially C1-4 alkyl, and each Q2 is hydrogen.
Both homopolymer and copolymer PPE are included. The preferred homopolymers are those containing 2,6-dimethyl-1,4-phenylene ether units. Suitable copolymers include random copolymers containing such units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene ether units. Also included are PPE containing moieties prepared by grafting vinyl monomers or polymers such as polystyrenes and elastomers, as well as coupled PPE in which coupling agents such as low molecular weight polycarbonates, quinones, heterocycles and formals undergo reaction in known manner with the hydroxy groups of two poly(phenylene ether) chains to produce a higher molecular weight polymer, provided a substantial proportion of free OH groups remains. Also included are PPE""s containing a functional endgroup, obtained from reaction with a reactive compound having the functional endgroup.
The low molecular weight PPE generally have a number average molecular weight within the range of about 1250 to about 7000 and a weight average molecular weight within the range of about 2500 to about 15,000, as determined by gel permeation chromatography, with a preferred number average molecular weight within the range of about 1750 to about 4000 and a weight average molecular weight within the range of about 3500 to about 9,000, as determined by gel permeation chromatography. Alternatively, the intrinsic viscosity (hereinafter xe2x80x9cI.V.xe2x80x9d) of the low molecular weight PPE is most often in the range of about 0.08-0.16 dl/g., preferably in the range of about 0.10-0.14 dl/g., as measured in chloroform at 25xc2x0 C.
The PPE are typically prepared by the oxidative coupling of at least one monohydroxyaromatic compound such as 2,6-xylenol, 2,3,6-trimethylphenol, or mixtures of the foregoing. Catalyst systems are generally employed for such coupling and they typically contain at least one heavy metal compound such as a copper, manganese, or cobalt compound, usually in combination with various other materials.
It will be apparent to those skilled in the art from the foregoing that the PPE contemplated in the present invention include all those presently known, irrespective of variations in structural units or ancillary chemical features.
The polymerization of the phenolic monomer may be carried out by adding the phenolic monomer or monomers to a suitable reaction solvent and preferably, a copper-amine catalyst. It is preferred to carry out the polymerization in the presence of a cupric or cuprous salt-secondary amine catalyst such as, for example, cupric chloride and di-n-butylamine. The polymerizations are advantageously carried out in the presence of an inorganic alkali metal bromide or an alkaline earth metal bromide. The inorganic bromides may be used at a level of from about 0.1 mole to about 150 moles per 100 moles of phenolic monomer. These catalyst materials are described in U.S. Pat. No. 3,733,299 (Cooper et al.). Tetraalkylammonium salts may also be employed as promoters if desired. These promoters are disclosed in U.S. Pat. No. 3,988,297 (Bennett et al.).
The primary, secondary or tertiary amine component of the catalyst complex generally correspond to those disclosed in U.S. Pat. Nos. 3,306,874 and 3,306,875 (Hay). Illustrative members include aliphatic amines, including aliphatic mono- and di-amines, where the aliphatic group can be straight or branched chain hydrocarbon or cycloaliphatic. Preferred are aliphatic primary, secondary and tertiary monoamines and tertiary diamines. Especially preferred are mono-, di- and tri(lower) alkyl amines, the alkyl groups having from 1 to 6 carbon atoms. Typically, there can be used mono-, di- and tri-methyl, ethyl, n-propyl i-propyl, n-butyl substituted amines, mono- and di-cyclohexylamine, ethylmethyl amine, morpholine, N-(lower) alkyl cycloaliphatic amines, such as N-methylcyclohexylamine, N,Nxe2x80x2-dialkylethylenediamines, the N,Nxe2x80x2-dialkylpropanediamines, the N,N,N,xe2x80x2-trialkylpentanediamines, and the like. In addition, cyclic tertiary amines, such as pyridine, alpha-collidine, gamma picoline, and the like, can be used. Especially useful are N,N,Nxe2x80x2,Nxe2x80x2-tetraalkylethylenediamines, butane-diamines, and the like.
Mixtures of such primary, secondary and tertiary amines may be used. A preferred mono alkyl amine is n-butyl amine; a preferred dialkyl amine is di-n-butyl amine; and a preferred trialkyl amine is triethylamine. A preferred cyclic tertiary amine is pyridine. The concentration of primary and secondary amine in the reaction mixture may vary within wide limits, but is desirably added in low concentrations. A preferred range of non-tertiary amines comprises from about 2.0 to about 25.0 moles per 100 moles of monovalent phenol. In the case of a tertiary amine, the preferred range is considerably broader, and comprises from about 0.2 to about 1500 moles per 100 moles of monovalent phenol. With tertiary amines, if water is not removed from the reaction mixture, it is preferred to use from about 500 to about 1500 moles of amine per 100 moles of phenol. If water is removed from the reaction, then only about 10 moles of tertiary amine, e.g., triethylamine or triethylamine, per 100 moles of phenol need be used as a lower limit. Even smaller amounts of tertiary diamines, such as N,N,Nxe2x80x2Nxe2x80x2-tetramethylbutanediamine can be used, down to as low as about 0.2 mole per 100 moles of phenol.
Typical examples of cuprous salts and cupric salts suitable for the process are shown in the Hay patents. These salts include, for example, cuprous chloride, cuprous bromide, cuprous sulfate, cuprous azide, cuprous tetramine sulfate, cuprous acetate, cuprous butyrate, cuprous toluate, cupric chloride, cupric bromide, cupric sulfate, cupric azide, cupric tetramine sulfate, cupric acetate, cupric butyrate, cupric toluate, and the like. Preferred cuprous and cupric salts include the halides, alkanoates or sulfates, e.g., cuprous bromide and cuprous chloride, cupric bromide and cupric chloride, cupric sulfate, cupric fluoride, cuprous acetate and cupric acetate. With primary and secondary amines, the concentration of the copper salts is desirable maintained low and preferably varies from about 0.2 to 2.5 moles per 100 moles of monovalent phenol. With tertiary amines, the copper salt is preferable used in an amount providing from about 0.2 to about 15 moles per 100 moles of the monovalent phenol.
Cupric halides are generally preferred over cuprous halides for the preparation of the copper amine catalyst because of their lower cost. The use of the copper (I) species also greatly increases the rate of oxygen utilization in the early stages of the polymerization reaction and the lower oxygen concentration in the head space of the reactor helps in reducing the risk of fire or explosion in the reactor. A process for the preparation and use of suitable copper-amine catalysts is in U.S. Pat. No. 3,900,445 (Cooper et al.).
A faster initial reaction rate with the copper (I) based catalyst also results in less accumulation of unreacted monomer and a reduction in the amount of undesirable tetramethyldiphenylquinone produced. The tetramethyldiphenylquinone, a backward dimer, is believed to incorporate into the PPE through equilibration reactions. The equilibration reactions lead to a drop in the intrinsic viscosity of the PPE due to the decrease in molecular weight of the PPE from the incorporation of the dimer. Minimization of the tetramethyldiphenylquinone during the oxidation coupling is desirable so as to avoid the drop in molecular weight and the accompanying difficulties in having to build to a higher than desired molecular weight to offset the loss during equilibration of the backward dimer. It was unexpectedly found that the present invention affords a process in which the PPE in the reaction mixture shows less than a 10% drop, preferably less than a 5% drop, most preferably less than a 3% drop in I.V. during an equilibration step after the oxidative polymerization of the phenolic monomers.
The polymerization reaction is preferably performed in a solvent. Suitable solvents are disclosed in the above-noted Hay patents. Aromatic solvents such as benzene, toluene, ethylbezene, xylene, and o-dichlorobenzene are especially preferred, although tetrachloromethane, trichloromethane, dichloromethane, 1,2-dichloroethane and trichloroethylene may also be used. The weight ratio between solvent and monomer is normally in the range from 1:1 to 20:1, ie. up to a maximum 20-fold excess of solvent. The ratio between solvent and monomer is preferably in the range from 1:1 to 10:1 by weight.
One unexpected advantage of the present process to make low intrinsic viscosity PPE is that a higher solids loading is possible as compared to processes that make higher (i.e.  greater than 0.28 I.V.) PPE. Without the increased solution viscosity build that concomitantly accompanies high molecular weight polymer, the final solids concentration can be increased by at least 20%, with increases of 30% or more possible. Thus, the present process affords a method for increased reactor utilization and productivity without increasing the size or number of the reactor vessels.
The process and reaction conditions for the polymerization, such as reaction time, temperature, oxygen flow rate and the like are modified based on the exact target molecular weight desired. The endpoint of the polymerization is conveniently determined with an in-line viscosity meter.
Although other methods such as making molecular weight measurements, running to a predetermined reaction time, controlling to a specified endgroup concentration, or the oxygen concentration in solution may also be utilized.
The temperature to carry out the polymerization stage of the invention generally ranges from about 0xc2x0 C. to about 95xc2x0 C. More preferably, the temperature range is from about 35xc2x0 C. to about 45xc2x0 C. with the higher reaction temperature near the end of reaction. At substantially higher temperatures, side reactions can occur leading to reaction by-products and at temperatures substantially lower, ice crystals form in the solution.
Many diverse extractants or chelating agents may be used in the practice of the invention to complex with the catalyst after the end of the polymerization reaction. For example, sulfuric acid, acetic acid, ammonium salts, bisulfate salts and various chelating agents may be used. When these materials are added to a PPE reaction solution, the copper-amine catalyst becomes poisoned and further oxidation does not take place. Many different materials may be used but it is preferred to employ those chelating agents that are disclosed in U.S. Pat. No. 3,838,102 (Bennett et al.).
The useful chelating agents include polyfunctional carboxylic acid containing compounds such as, for example, sodium potassium tartrate, nitrilotriacetic acid (NTA), citric acid, glycine and especially preferably they will be selected from polyalkylenepolyamine polycarboxylic acids, aminopolycarboxylic acids, aminocarboxylic acids, aminopolycarboxylic acids, aminocarboxylic acids, polycarboxylic acids and their alkali metal, alkaline earth metal or mixed alkali metal-alkaline earth metal salts. The preferred agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid and their salts. Especially preferred are ethylenediaminotetraacetic acid or a mono-, di-, tri- and tetrasodium salt thereof and the resulting copper complex can be referred to as a copper carboxylate complex.
The chelated metallic catalyst component can be extracted with the water produced in the polymerization reaction by through the use of a liquid/liquid centrifuge. The preferred extraction liquid for use in the process of the invention is an aqueous solution of lower alkanol, i.e., a mixture of water and an alkanol having from 1 to about 4 carbon atoms. Generally from about 1% to about 80% by volume of an alkanol or glycol may be employed. These ratios may vary from about 0.01:1 to about 10:1 parts by volume of aqueous liquid extractant to discrete organic phase.
The reaction media generally comprises an aqueous environment. Anti-solvents can also be utilized in combination with the aqueous media to help drive the precipitation of the copper (I) species. The selection of an appropriate anti-solvent is based partially on the solubility co-efficient of the copper (I) species that is being precipitated. The halides are highly insoluble in water, log K[sp]values at 25xc2x0 C. are xe2x88x924.49, xe2x88x928.23 and xe2x88x9211.96 for CuCl, CuBr and Cul, respectively. Solubility in water is increased by the presence of excess of halide ions due to the formation of, e.g., CuCl2, CUCl3, and CuCl4 and by other complexing species. Non-limiting examples of anti-solvents would comprise low molecular weight alkyl and aromatic hydrocarbons, ketones, alcohols and the like which in themselves would have some solubility in the aqueous solution. One skilled in the art would be able to select an appropriate type and amount of anti-solvent, if any was utilized.
One unexpected advantage of the present invention to make low molecular weight PPE (i.e. PPE having an I.V. in the range of about 0.08-0.16 dl/g.) is the reduction in I.V. variation and molecular weight of the PPE after the end of reaction. In the processes of the prior art to make higher intrinsic viscosity resin, i.e. I.V. greater than 0.28 dl/g., after the end of reaction the PPE is held at elevated temperature, typically between about 45xc2x0 C. to about 70xc2x0 C. for between about 45 to 90 minutes, while the catalyst chelating species as described above is added and allowed to react. During this equilibration process, the previously described backward dimer phenols that are reaction by-products of the oxidation process incorporate into the polymer backbone resulting in a decrease in the molecular weight and I.V. of the PPE. To illustrate this decrease, a PPE targeted to have an I.V, of 0.48 dl/g at the end of reaction will drop to an I.V. of about 0.38 dl/g after equilibration. Conversely, in the present invention, a PPE having a target end of run I.V. of about 0.113 dl/g, after equilibration will have an I.V. of about 0.115 dl/g. It should be apparent that the present invention affords a method to prepare a PPE that has less than about a 10% drop, preferably less than about a 5% drop, and most preferably less than about a 3% drop in I.V. during equilibration after the end of reaction.
After removal of the catalyst, the PPE containing solution is concentrated to a higher solids level as part of the isolation of the PPE. Precipitation using standard non-solvent techniques typical for PPE having I.V.""s greater than 0.28 dl/g are not generally useful for isolation of low molecular weight PPE due to the small PPE particle size and friability of the particles. Very low yields are obtained with undesirable fractionation of oligomeric species. A total isolation process is preferred for isolating the PPE. As part of the total isolation, a portion of the solvent is preferably removed in order to reduce the solvent load on the total isolation equipment.
Concentration of the PPE containing solution is accomplished by reducing the pressure in a solvent flash vessel while preferably increasing the temperature of the PPE containing solution. Pressures of about 35 to 50 bar are desirable with solution temperatures increased to at least 200xc2x0 C., preferably of at least 230xc2x0 C. A solids level of PPE of at least 55%, preferably of at least 65% or higher is desirable.
The isolation of the PPE is typically carried out in a devolatilizing extruder although other methods involving spray drying, wiped film evaporators, flake evaporators, and flash vessels with melt pumps, including various combinations involving these methods are also useful and in some instances preferred. As previously described, total isolation is preferably from the viewpoint that oligomeric species are not removed to the same degree as with precipitation. Likewise, isolation yields are extremely high and are near quantitative. These techniques require however that the catalyst removal be completed in the prior process steps as any catalyst remaining in solution will necessarily be isolated in the PPE.
Devolatilizing extruders and processes are known in the art and typically involve a twin-screw extruder equipped with multiple venting sections for solvent removal. In the practice of the present invention, the preheated concentrated solution containing the PPE is fed into the devolatilizing extruder and maintained at a temperature less than about 275xc2x0 C., and preferably less than about 250xc2x0 C., and most preferably between about 185-220xc2x0 C. with pressures in the vacuum vent of less than about 1 bar. The resultant solvent level is reduced to less than about 1200 ppm, preferably less than about 600 ppm, and most preferably less than about 400 ppm. Furthermore, it was unexpected that temperatures as low as less than 250xc2x0 C. and preferably between about 185-220xc2x0 C. would be useful and preferred as current PPE having an I.V. of  greater than 0.28 dl/g generally require a temperature of 300xc2x0 C. or higher in similar total isolation processes.
Another unexpected result obtained through the use of a devolatilizing extruder was the extremely high yield of PPE achieved in the process. For example, a PPE yield of over 99% was obtained even for PPE having a low I.V. whereas in the precipitation process known in the art, the yield of similar low I.V. PPE was less than 90%. Thus, the present process comprising a devolatilizing extruder affords a method to prepare low molecular weight polyphenylene ether resin, typically within the intrinsic viscosity range of about 0.08 dl/g to about 0.16 dl/g, in a yield of over 90%, preferably over 95%, more preferably over 98% and most preferably over 99%, based upon the amount of monovalent phenol utilized in the oxidative coupling.
When using a devolatilization extruder for the total isolation of the PPE, it was found that traditional underwater or water spray cooling of strands of extrudate followed by chopping the extrudate into pellets gave unacceptable results presumably due to the low melt strength and inherent brittle nature of low molecular weight PPE. It was found that special pelletization techniques can overcome these difficulties. Useful techniques include die-face pelletization, including underwater pelletization and flaking, declining angle strand pelletization using water spraying, and vibration drop pelletization with underwater pelletization especially suitable.
It was unexpectedly found that underwater pelletization resulted in a significantly lower color in the PPE as compared to the standard stranding with water/air cooling followed by pelletization techniques. Yellowness index (YI) numbers of less than 30, and even less than 25 are achievable as compared to YI greater than 50 achieved with the standard stranding technique. It should be apparent that the present process affords a method of preparing a PPE with a YI of less than about 30, preferably less than about 25.
Another unexpected benefit of underwater pelletization of PPE, especially low I.V. PPE, is that very low (less than about 3% by weight) fines, defined as pellets (i.e. particles) of less than 850 microns in size, could be obtained. It should be clear that the present invention includes a method to reduce the number of fines having a particle size less than about 850 micron in polyphenylene ether wherein the method comprises underwater pelletization of the polyphenylene ether resin. A preferred embodiment includes a method to reduce the number of fines having a particle size less than about 850 micron to less than about 3%, preferably less than about 1.5% by weight based on the total weight of the pellets.
The collected PPE pellets can be dried using techniques standard in the art including centrifugal dryers, batch or continuous oven dryers, fluid beds, and the like. Determination of an appropriate set of conditions can be readily determined by one of skill in the art without undue experimentation.
All patents cited by reference are incorporated herein by reference.
In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation.